The invention relates to plastic solid or hollow plastics profiles intended, in particular, to absorb tensile, bending and/or pressure loads, such as are used, in particular, as insulating segments in composite profiles comprising metallic profiled elements.
Known profiles of this type are disclosed, for example, in DE 32 03 631 A1 or DE 38 01 564 A1 and serve as heat-insulating profiles located between metallic profiled elements and are made of high-strength plastics material having poor thermal-conduction properties, for example, a fiberglass-reinforced polyamide. These composite profiles are primarily used in the production of window or facade elements.
These composite profiles and consequently the solid or hollow profiles of plastics material are exposed to considerable influences, for example, wind stresses, perpendicular loads, particularly those caused by the weight of the window glass, and stresses primarily due to temperature differences between the outer and inner metallic profiled elements of the composite profile. The less change occurring in the plastics material of the insulating profiles under climatic conditions such as temperature and air humidity, the lower the stresses that result at the interface between plastics profile and metallic profile.
Hitherto attempts have been made to influence the expansion characteristics of the plastics materials in a favorable manner, ie to reduce their coefficients of expansion, by using plastics materials having higher filler contents, particularly contents of mineral reinforcing and filling materials, especially glass fibers.
However, higher filler contents produce a number of drawbacks. In addition to increased raw-material costs and the greater weight of the insulating profiles, problems arise in processing the raw material, particularly as regards wear and productivity. Following extrusion and solidification, fiberglass-reinforced plastics materials can exhibit undesirable anisotropies, internal residual stresses, greatly reduced ductility and, in particular, higher heat conductivity than the pure plastics material.
In DE 38 01 564 Al, the attempt is made to reduce the heat conductivity of the insulating profile by incorporating small hollow spheres of glass. However, the technology has its limits, and, in view of the more stringent legislative demands regarding energy saving, likewise imposed by the manufacturers of composite profiles, this technology no longer satisfies requirements in all cases.
It is an object of the invention to develop the above solid or hollow profile such that the drawbacks described above are reduced as far as possible.
This object is achieved in the aforementioned solid or hollow plastics profile in that it has a surface layer of a solid, non-porous first plastics material and a core region comprising a fine-pored, closed-cell cellular structure of a second plastics material.
The said object is further achieved by a hollow profile, which is characterized by a surface layer of a solid, non-porous first plastics material, a core region comprising a fine-pored, closed-cell cellular structure of a second plastics material, and an inner surface layer defining the hollow chamber and composed of a solid, non-porous third plastics material.
The cellular structure of the core region is a closed-cell structure so that a large number of insulating gas volumes is present in the plastics profile. Optimal heat transfer resistance is thus obtain. The fine-pored and closed-cell properties of the core region are also an important factor, since the mechanical properties will not weaken as the density decreases but will remain largely at a constant value.
The profiles of the invention can be manufactured in a manner similar to that described in DE 32 03 631 C2 and DE 19 510 944 C1. The fine-pored core is obtained by foaming the second plastics material with conventional agents such as liquid CO2, nitrogen or azodicarbonamide.
The restriction of the solid, non-porous first plastics material to the formation of a surface layer around the plastics profile and the use of a core region of a fine-pored cellular structure cause considerable reduction in the overall heat conductivity of the profile. The reduction of the heat conductivity is substantially due to the reduction in density of, ie the gas content in, the core region. This in turn leads to a reduction in the weight of the profile and involves considerable savings of raw material during production of the plastics profile. The possible savings in raw material are up to 60% depending on the wall thickness of the surface layer(s) and the particular application. For given profile dimensions, there is achieved a considerable reduction in weight per meter run with only slight detriment to the rigidity behavior (coefficient of transverse bending).
The profile thickness can be increased, for a given weight per meter run, over that of conventional profiles, and this gives rise to considerably higher rigidity or bending strength of the plastics profile. Surprisingly, only a slight increase in the wall thickness can result in, say, twice the coefficient of transverse bending, and this is particularly due to the use, in the core region, of fine-pored structures whose mechanical properties are not linearly related to density as is commonly encountered with freely foamed, large-pored cellular structures of the prior art.
In order to acquire optimal mechanical properties, particularly strength properties, care should be taken to ensure that the porosity or the cellular structure is uniform across substantially the entire cross-section of the core region. In particular, it is important to keep the cell size within a specific range, for example, that recommended below, and to avoid the occurrence of coarser cells at discrete points of the cross-section.
In the case of hollow chamber profiles having an inner surface layer of solid plastics material, the structure of the profile will preferably be such that the core region including its cellular structure will be completely enclosed by the surface layer and the inner surface layer defining the hollow chambers or cavities.
In this case, the surface layer, the core region, and the inner surface layer preferably form a sandwich structure in at least some regions of the profile, said sandwich structure being such that the surface layer, the inner surface layer, and the core region enclosed thereby form layers which are disposed substantially parallel to each other.
The first, second, and third plastics materials used for the production of the profiles of the invention can be the same or different and can contain reinforcing materials, fillers, modifiers, and/or additives. The reinforcing materials may be short, long, and/or continuous fibers, particularly glass, carbon, aramide, or natural fibers. Suitable fillers are glass spheres, hollow glass spheres, wollastonite, mica, and nanoparticles.
The group of modifiers includes impact modifiers, ultraviolet heat stabilizers, conductive substances, nucleating agents, coupling agents, etc.
In the case of profiles having a molded-on flange to be engaged by a corresponding groove in the metallic profiles of a heat-insulating compound profile, it is recommended to provide the surface of the flange, at least in certain regions, with a fine-pored coating by, say, co-extrusion. This makes it possible to make the flange somewhat undersize relatively to the groove in the respective metallic profile to be engaged thereby, and the groove walls can be pressed against the flange by a knurling operation so as to deform said fine-pored coating. This produces a particularly good positive fit between the flange of the profile and the groove in the metallic profile.
The average cell size (diameter) of the cellular structure in the core region should, in particular, be in the range of from 0.005 to 0.1 mm, preferably from 0.02 to 0.05 mm. Within these ranges there is achieved an optimum of mass economy without weakening the mechanical properties.
The density of the material in the core region can be up to ca 60% less than that of the raw material.
The plastics materials suitable for use as raw materials in the production of the profiles of the invention, range from thermoplastic and duroplastic to elastomeric plastics materials or mixtures thereof.
Normally, the same raw material will be used for the first, second, and optionally third plastics materials, an approprate procedure being adopted such that the solid surface layer will be formed quasi automatically so that it will not be absolutely necessary to employ a co-extrusion process for the formation of the solid surface layer adjacent the porous core region.
In special cases the core region of the profile of the invention will be composed of a second plastics material differing from the plastics material of the surface layer (first plastics material). This presents the possibility of using a high-grade plastics material for the formation of the surface layer, whilst in the core region a substantially cheaper plastics material can be used. The same applies to the third plastics material.
The profiles of the invention are, for particular applications, completely, or in at least some areas, surface-coated with primers, adhesive coating compositions, and/or conductive lacquers. The profiles of the invention can in this way be prepared for secondary treatment processes such as powder wet coating or anodizing processes.
The profiles of the invention are particularly intended for use as heat-insulating profiles in the production of metal/plastics composite profiles.
The invention finally relates to heat-insulated composite profiles, particularly for use in the manufacture of windows, doors, facades or the like having an inner and an outer metallic profile, which metallic profiles are interconnected by at least one plastics profile of the invention as previously described, by which means said metallic profiles are kept at a specified distance from each other.
These and other advantages of the invention are explained in greater detail below with reference to the drawings.